1. Field of the Invention
The present invention relates to a driving circuit and method for a fan, and more particularly, to a driving circuit and method utilizing a pulse frequency modulation technique to operate the fan with a plurality of operational modes.
2. Description of the Prior Art
A motor is an electronic device for transferring electrical energy into dynamic energy, such as a DC motor, an AC motor or a stepper motor, etc. The DC motor is frequently utilized in non-sophisticated control devices, such as a fan. Generally, the DC motor rotates based on a current passing through coils of a stator of the DC motor to generate different amounts or polarized directions of magnetic force to attract or repel a permanent magnet on a rotor of the DC motor to make the motor rotate.
Please refer to FIG. 1, which illustrates a schematic diagram of a conventional motor driving circuit 10. As shown in FIG. 1, the motor driving circuit 10 utilizes a linear voltage driving process to correspondingly drive a fan 12 for rotation. The motor driving circuit 10 receives an input voltage source VIN, and a voltage drop is correspondingly generated to render an output voltage VOUT to the fan 12, wherein the voltage drop is a difference between the input voltage source VIN and the output voltage VOUT. Please refer to FIG. 2, which illustrates a schematic diagram of temperature values versus rotational speeds of the motor driving circuit 10 shown in FIG. 1, wherein the motor driving circuit 10 is an electrical chip circuit labeled GR8030, the X-axis represents the surrounding temperature values of the fan 12 (or via realization as a conduction voltage/current of the fan 12), and the Y-axis represents relative rotational speeds of the fan 12 (i.e. a percentage of the maximum rotational speed of the fan 12). As shown in FIG. 2, while a user initiates the motor driving circuit 10, the temperature value of the fan 12 is a lower value and the motor driving circuit 10 drives the fan 12 with a larger initial rotational speed. For example, the fan 12, as shown in FIG. 2, increases the rotational speed from 60% maximum rotational speed to 80% maximum rotational speed, and returns to 10% maximum rotational speed after waiting a predetermined period. Under such circumstances, the fan 12 maintains the 10% maximum rotational speed as a minimum rotational speed without changes. When the fan 12 is operated with an increased temperature value such as 30 degrees, the motor driving circuit 10 may correspondingly increase the relative rotational speed of the fan 12. Preferably, increases of the relative rotational speed and increases of the driving voltage form a linear relationship, which means that when the surrounding temperature value of the fan 12 is a larger value, the relative rotational speed of the fan 12 is faster, such that the fan 12 can effectively eliminate heat generation while being operated. When the surrounding temperature value of the fan 12 continuously increases to 100 degrees, the fan 12 may be operated with the maximum rotational speed. In that, when the fan 12 is operated with the maximum rotational speed for a while and the temperature value continuously increases to a predetermined maximum temperature as 115 degrees without reduction, the motor driving circuit 10 may determine the fan 12 as being overheated, i.e. an electronic system comprising the fan 12 may be overloaded, such that the motor driving circuit 10 may process an overheated protection mechanism for the fan 12. However, the prior art merely adjusts the input voltage VIN for linear increasing/decreasing the driving voltage to correspondingly increase/decrease the rotational speed of the fan 12, and lacks of flexibility to adjust the rotational speed of the fan 12 via other operations or control signals, so as to adaptively apply the fan 12 into different environmental conditions to meet specific requirements. Thus, the application of the motor driving circuit 10 can be limited.
Therefore, it has become an important issue to provide a driving circuit and method for a fan via different operational modes, so as to comply with different environmental conditions and particular requirements.